In recent years, recording media such as hard disks have been desired to have an outstandingly increased recording capacity. To respond to the demands, developments of magnetic recording media with high recording capacity are proceeding.
In a magnetic recording medium used in conventional hard disks, a predetermined region of a thin film including polycrystals of magnetic fine particles is used as one bit for recording. In order to increase recording capacity of a magnetic recording medium, the recording density should be increased. In other words, it is necessary to reduce the recording mark size which is usable for recording of one bit. However, when the recording mark size is simply reduced, the influence of noise which depends on the shapes of magnetic fine particles becomes nonnegligible. If the particle size of magnetic fine particles is reduced to lower the noise, a problem of thermal fluctuation occurs, which makes it impossible to maintain recorded data at a room temperature.
In order to avoid these problems, a bit patterned recording medium (BPR) has been proposed, in which the recording material is separated by a nonmagnetic material in advance, and a single magnetic dot is used as a single recording cell to perform read and write.
In magnetic recording media installed in HDDs, there is an arising problem of the interference between adjacent tracks which inhibits improvement in track density. Particularly, reducing a fringe effect of a write head field is a significant technical problem to be solved. To solve this problem, there has been developed a discrete track recording-type patterned medium (DTR medium), in which the magnetic recording layer is processed so that the recording tracks are physically separated from each other. In the DTR medium, it is possible to reduce side erase which erases information in the adjacent tracks in writing and side read which reads information in the adjacent tracks in reading. On this account, the DTR medium is promising as a magnetic recording medium capable of providing a high recording density. Incidentally, it should be noted that the term “patterned medium” as used herein in a broad sense includes the bit patterned recording medium and DTR medium.
In case of manufacturing such a patterned medium, it is significant to form tracks or dots in good shapes. In particular, if roughness is produced along the outlines of tracks or dots (edge roughness), error rates in reading and writing information will be increased. Therefore, such edge roughness should be restricted as far as possible.
In the manufacturing method described in Jpn. Pat. Appln. KOKAI Publication No. 2009-301655, a mask used to form patterns on a magnetic recording layer is removed by dry etching. According to the method, while a fringe property can be improved, there is a possibility that the pattern of the magnetic recording layer is damaged by the dry etching conducted to remove the mask.
On the other hand, in the method described in Jpn. Pat. Appln. KOKAI Publication No. 2008-53473, amorphous MgO or amorphous Mo is used as a mask, and the mask is removed by a wet process using a solution. In such a method, while the damage to the magnetic recording layer due to the removal of the mask can be reduced, there is a possibility that the edge roughness is produced in the patterned magnetic recording layer.